This invention relates to scroll fluid apparatus suitable for use for refrigerating apparatus, air compressors or expanders.
Generally a scroll fluid apparatus comprises an orbiting scroll member and a fixed or stationary scroll member, with the orbiting scroll member including an end plate and a wrap in the form of an involute curve or the like disposed in an upright position on the end plate, and the stationary scroll member including an end plate and a wrap in the form of an involute curve or the like disposed in an upright position on the end plate and formed with an exhuast port near the center of the end plate and with a suction port at an outer portion of the end plate, the orbiting and the stationary scroll members being assembled with the wraps facing inwardly and meshing with each other and contained in a casing having a suction pipe and a discharge pipe both connected to the casing.
A scroll fluid apparatus of the aforementioned type is disclosed in, for example, U.S. Pat. No. 3,884,559, wherein an Oldham'coupling mechanism is mounted between the orbiting scroll member and a frame or between the orbiting scroll member and the stationary scroll member to keep the oribiting scroll member from rotating on its own axis, and the oribiting scroll member is kept in engagement with a crankshaft which moves the oribiting scroll member in orbiting movement without rotating on its own axis to compress gas in sealed spaces defined between the two scroll members and discharge compressed gas through the exhaust port.
In a scroll fluid apparatus of the aforementioned type, one of the sealed spaces is defined by an inner wall surface of the wrap of the stationary scroll member, an outer wall surface of the wrap of the orbiting scroll member and end surfaces of the end plates of the two scroll members, and the other sealed space is defined by an outer wall surface of the wrap of the stationary scroll member, an inner wall surface of the orbiting scroll member and the end surfaces of the end plates of the two scroll members, so that the two sealed spaces can be symmetrical. Thus, two suction chambers are formed before the two sealed spaces are formed and each have a suction passage connected to the suction port. It is essential that these suction passages each have a predetermined passage area. If the passage areas of the suction passages were reduced, the suction pressure would suffer a loss of pressure and a variation in pressure. Also, if the two suction passages are inordinately distinct from each other in the area of passage, the loss of pressure and the variation in pressure would differ from one suction passage to the other suction passage. The result of this would be that pressure difference would be produced between the two sealed space in the same compression stroke and cause a leak to occur between the two chambers, thereby increasing power required for operating the compressor.
It is generally desired that an overall compact size and a light weight be obtained in this type of scroll fluid apparatus. The compressor section of a fluid scroll apparatus is composed of the orbiting and the stationary scroll members which are circular at the outer periphery, so that is is possible to reduce the size of the apparatus by reducing the diameter of the end plates which are in the form of a disc.
Japanese Patent application Laid-Open No. 51986/80 and No. 51987/80, both relate to a scroll fluid apparatu in which the end plate of the orbiting scroll member is off-center, to reduce the diameter of the casing. More specifically, the end plate of the orbiting scroll member has a diameter 2r+R, wherein r is the distance between the center of the base circle of the spiral wrap and the outermost end of the spiral wrap, and R is the length of a crank arm, and the center of the end plate of the oribiting scroll member is displaced by R/2 from the center of the base circle of the spiral wrap in a direction opposite the direction of the outermost end of the spiral wrap from the center of the base circle, while the center of the housing is displaced by R/2 from the centers of the base circles of the spiral wraps of the scroll members in the direction of the outermost end of the spiral wraps, to thereby reduce the diameter of the housing. However, no express mention is made in the Japanese applications with regard to obtaining a predetermined area required for the suction passages.